Two-part preformed coils



Aug. 21, 1951 R. P. HANNA Two-PART PREFORMED coms Filed Aug. 6, 1949Commutoor End Frome Side INVENTOR Raymond P.Honnu.

WITNESSES:

ATTORNEY Patented Aug. 21, 1951 TWO-PART PREFORMED COILS Raymond P.Hanna, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation,East Pittsburgh, Pa., a corporation of Pennsylvania Application August6, 1949, Serial No. 108,963

My invention relates to electrical coils which are preformed so as to bemountable upon the shank of a pole-piece or magnetizable coremember, orupon a suitable mandrel or support of some other kind. Although notnecessarily limited thereto, my invention relates more particularly toshunt-type field-coils for dynamo-electric machines of intermediatevoltageratings.

An object of my invention is to provide twopart preformed coils,consisting of an inner coil which is completely covered with one or morelayers of ground-insulation, around which is wound a smaller outer coilhaving no groundinsulation, said outer coil being stepped or spaced backfrom the side or sides where grounded supports are likely to be present,so that this stepped-back space will provide a surfacecreepage-distance', over the surface of the ground-insulation, forinsulating` the outer coil from ground. The two coil-portions may beelectrically insulated from each other, but if they are parts of asingle composite coil, the conductors of the inner and outercoil-portions will be electrically and thermally continuous. Since theouter coil is wound over the ground-insulation of the inner coil, itcompresses that groundinsulation, so as to facilitate heat-nowtherethrough, while at the same time providing a relatively cool metalmember in close :Contact with the outer surface of theground-insulation, which also has advantages in facilitatingheattransfer through the thickness of the groundinsuation. The outercoil is thus air-cooled, so that it serves as a cooling-means for theinner coil, with heat owing through the thickness of theground-insulation between the two coils. When the conductors of theinner and outer coils are electrically and thermally continuous, a veryconsiderable part of the heat will also ow lengthwise through saidelectrically and thermally continuous conductors of the two coils.

Heretofore, field-coils for dynamo-electric machines have had to beeither completely surrounded with ground-insulation, or they have had tobe specially constructed, involving many costly manufacturing-steps,including the cutting of a window through the ground-insulation, so asto expose a portion of the coil underneath the ground-insulation, tofacilitate the cooling of the coil. My present invention is animprovement over both of these previous coil-designs, runningconsiderably cooler than either one of the previous designs, whilehaving 1 Claim. (Cl. 175-21) a reasonable manufacturing cost, la durablefinish (as compared with the cut insulation of the window coils), andhaving a pleasing external appearance.

With the foregoing and other objects in view, my invention consists inthe combinations, systems, structures, parts, and methods of design `andassembly, hereinafter described and claimed, and illustrated in theaccompanying drawing, wherein Figure 1 is a plan view of a finished coilembodying my invention,

Fig. 2 is an enlarged cross sectional View thereof, on a plane indicatedby the line II-II in Fig. 1, and

Fig. 3 is an end View thereof.

It will be noted, more particularly from Fig. 2, that the illustratedform of embodiment of my invention is really a composite coil, havingtwo parts, although the two parts may be electrically independent. Onepart of said composite coil comprises a plurality of turns of aconductor 5, which is wound into an inner coil 6 having a desired numberof turns, and having suitable turn-to-turn insulation which is generallyin the form of a thin insulating .covering 1 surrounding the conductor5, and represented, in Fig. 2, simply by the thickness of a line. I haveillustrated my invention as using a small round wire for the conductor5, but this is only by way of illustration, as the conductor could be astrap of either square or rectangular cross section, as is well knownand commonly practiced in the coil-winding art. The inner coil 6 iscompletely wrapped or enclosed in one or more layers ofground-insulation 8, having the necessary thickness to provide aninsulatingbarrier between the conductor 5 of the inner coil `6 and anygrounded surface, such as 9 (Fig. 3), against which one side of the coilmay abut.

The other part of the composite coil comprises one or more turns of aconductor II, wound as an outer coil I2 around the periphery of theground-insulation 8. This outer coil I2 is usually, althoughtheoretically not absolutely necessarily, wound with a smaller number ofturns than the inner coil 6. The Outer coil I2, in the preferred form ofmy invention, is stepped back on both sides, so that it is not as wideas the inner coil E, these stepped-back spaces providing surfacescreepage-distances, such as that which is indicated in dotted lines atI3 in Fig. 2, for providing surface-creepage ground-insulation betweenthe conductor Il of the outer coil I2 and the surface-part of theground-insulation 8 which may be in contact with a grounded member suchas the member 9 in Fig. 3. If the outer coil I2 consists of more thanone layer, as is the case in the illustrated form of embodiment of myinvention, then its conductor I2 will have an insulating covering I4,similar to the covering 'I which has been described in connection withthe inner coil 6, for providing the necessary turn-to-turn insulation.

Before the outer coil I 2 is wound over the ground-insulation 8 whichencompasses the inner coil 6, one or more adherent tapes I arepreferably laid down, so that, when the winding of the outer coil I2 isfinished, these tapes I5 may be drawn around the coil to hold its wirestogether, as shown in Figs. 1 and 2. If the outer coil I2 is composed ofa number of turns, i-t is sometimes advantageous if the surface of itsconductor-insulation I4 is somewhat gummy or Sticky, so as to facilitateholding the wires together during the winding-process, .before the tapesI5 are drawn around the nished coil to hold it in shape.

The conductors 5 and I I of the two coils 6 and I2 may be one continuousconductor or, if more convenient, the inner coil may be irst formed,with only a sulicient length of conductor to leave short conductor-endsor terminals sticking out of the wrapped insulation 8, and then thestartingend of the conductor II for the second coil may be soldered tothe finish lead of the rst coil, so that the two conductors will beelectrically and thermally continuous. In some cases, however, the twocoils'G and I2 may be electrically separate from each other.

As shown more particularly in Fig. 3, after the composite coil, as justdescribed, has been completed, the under lead or starting-lead 5' of theinner coil 6 may be connected, by a suitable connector I6, to atermin-al cable I1, while the nish lead II of the outer coil I2 may beconnected, by a terminal-connector I8, to a second cable I9.

It will also vbe understood that the finished composite coil may besubjected to any desired impregnating or varnishing treatment, or thelike, as is well known in the art.

In appearance, my nnished composite coil is characterized by an innerpart, which is completely enclosed in the `ground-insulation taping 8,with a second part I2 projecting out from a part of the surface of theground-insulation taping 8, this second part being made up of onlylightly insulated conductors II. These conductors II are thus exposed tothe air, so that they are well cooled. This well-cooled outer coil vI2presses down tightly against a portion of the surface of theground-insulation taping 8, so that there is a fairly goodheat-transfer, through the thickness of the ground-insulation 8, fromthe inner coil 6 to the cooled outer coil I2. I have reason to believe,also, that a very considerable part of the total heat-transfer isconducted lengthwise through the electrically continuous Conductors 5and I I, so that the heat flows from the relatively hot inner conductors5, lengthwise through the conductor-length which separates the twocoils, and thence into the outer conductors II. In general, my improvedcoil has at least 20% more heat-transferring ability, for getting .heatlout of the inner coil 6, than is obtainable with either one of theprevious types of coils which have vbeen used for the same purpose.

While I have described and illustrated my invention in accordance with asingle specic illustrated form of design, with some suggestions as topossible alternatives and modifications, I wish it to be understood thatI am not limited to these precise details. I desire, therefore, that theappended claim shall be accorded the broadest construction consistentwith its language.

I claim as my invention:

A two-part composite preformed coil adapted to be mounted with at leastone side in contact with a grounded member; one part of said compositecoil comprising a plurality of turns of a conductor, wound into an innercoil, and having turn-to-turn insulation between adjacent turns, and atleast one layer of ground-insulation completely surrounding said innercoil; andthe other part of'said composite coil comprising at least oneturn of a conductor, wound as an outer coil around the periphery of saidground-insulation and stepped back from said side of saidgroundinsulation whereby to provide :a surface creepagedistance, at thatside ofthe ground-insulation, between the grounded member and the outercoil; the conductors of said inner and outer coils being electricallyand thermally continuousy whereby the two coils compose a singlecomposite coil, and whereby the outer coil serves as a, cooling-meansfor the inner coil.

RAYMOND P. HANNA.

REFERENCES CITEDl l The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,360,835 Kongsted et al Oct. 24,1944 2,436,188 Bilodeau Feb, 17, 1948 2,526,549 Freas, Jr I, Oct. 17,1950

